The present invention relates to a power distribution system, and more particularly, to an overload circuit interrupter capable of detecting overload and interrupting the overload circuit interrupter, and to a circuit breaker with the same.
Low voltage networks, typically 600 volts and below, are used to distribute electric power in a specified area, such as part of a city or an industrial or commercial area. Often, the cables in such networks are located underground. Typically, the network is designed to feed at more than one point, and therefore, has multiple sources. Occasionally, the cables have failed, due to various causes such as thermal degradation, age, moisture or rodent damage.
The networks are protected by circuit breakers. In order to isolate the faulty cable and therefore minimize disruption of the networks, cable limiters are provided at the ends of the cables. Cable limiters are fuse-like devices, which assure safe reactions to high voltage and low impedance faults, such as are created by phase-to-phase faults.
Wiring (miniature) circuit interrupters and current leakage circuit interrupter are commonly used devices for protecting people and property from fire and dangerous electrical faults. A wiring circuit interrupter is used to protect a power line. First, when excessive current passing through circuit breaker is converted to heat in the use of an electrical device, the circuit interrupter is tripped by a bending of bimetal in it. Second, when an electrical tool or other metallic object on the load shorts the power line, high current is passed through instantaneously. Therefore, bimetal in the circuit breaker is heated by high current, so the electrical device is interrupted by operation of an inner magnet of the circuit breaker.
It is known in the art that a current leakage circuit interrupter has the ability to detect current leakage, which may be present on the power line, and trip the circuit interrupter, so that the circuit interrupter prevents people from receiving an electric shock from the leakage current.
In America, ground fault circuit interrupters (GFCI) are required to be used, which contact people""s hands directly, in the wiring (miniature) circuit interrupter. The GFCI, which is able to detect leakage current with high sensitivity, belongs to the category of current leakage circuit interrupters. Thus GFCI must be installed in kitchens, bathrooms, parking places and basements, which easily may become damp and wet.
In spite of the wiring circuit interrupter and current leakage circuit interrupter, large numbers of fires occur all over the world every year. This is due to the fact that often an arcing type fault to ground occurs rather than a phase-to-phase fault. Arcing faults typically create current with low root mean square (RMS) value, which is below the thermal threshold for such circuit breakers. Even so, such arcs can cause damage or start a fire if they occur near combustible material.
Arcs are potentially dangerous due to the high temperatures. An arc, however, will only trip a GFCI when it produces sufficient current leakage to ground. In addition, an arc will trip a circuit breaker only if the current, flowing through the arc, exceeds the trip parameters of the thermal/magnetic mechanism of the breaker. Therefore, an additional type of protective device is needed to detect and interrupt arcs that do not fit these criteria. An arc detector whose output is used to trigger a circuit interrupting mechanism is referred to as an arc fault circuit interrupter (AFCI).
The U.S. Consumer Product Safety Commission (CPSC) estimated that 40% of fires in 1997 were caused by arc faults. Also, the National Electric Code (NEC) includes a regulation requiring installation of the AFCI in residential buildings from January 2002.
The causes of arc faults are numerous. For example, they include aged or worn insulation and wiring, mechanical and electrical stress caused by overuse, over currents or lightning strikes, loose connections, and excessive mechanical damage to insulation and wires.
Three types of arcing may occur in residential or commercial buildings: serial arcing, parallel arcing and ground arcing.
Serial (or contact) arcing occurs between two contacts in series with a load. The conductors comprising the cable are separated and surrounded by an insulator. A portion of the conductor is broken, creating a series gap in the conductor. Under certain conditions, arcing will occur across this gap, producing a large amount of localized heat. The heat produced by the arcing might be sufficient to break down and carbonize insulation close to the arcing. If the arc is allowed to continue, enough heat will be generated to start a fire. Under these conditions, current flowing through the arc is controlled by load.
Parallel (line) arcing is the second. Cable comprises electrical conductors covered by outer insulation and separated by inner insulation. Deterioration or damage to the inner insulation at any point may cause parallel fault arcing to occur between the two conductors. The inner insulation could have been carbonized by an earlier lightning strike to the wiring system, or it could have been cut by mechanical action such as a metal chair leg cutting into an extension cord.
Ground arcing occurring between a conductor and ground is the third. If the outer insulation used for protecting conductors is damaged, the conductor contacting ground due to a damaged portion will result in ground arcing.
Current flowing through the arcing may be changed by impedance because parallel arcing and ground arcing occur parallel to the load. Long time deterioration causes cable carbonization and damage to coating. The cable is further deteriorated by Joule heat, which is induced by arcing current. The arcing generates joule heat according to the ** in a relation of J (Joule heat)=I2(arcing current)xc3x97t(Time).
One major problem associated with any type of arc detection is false tripping. False tripping occurs when an arc detector produces a warning output, or disconnects a section of wiring from the voltage source, when a dangerous arcing condition does not actually exist. This problem is caused by the fact that an arc signal (arcing current and arcing voltage) is not generated in the form of a correct sine wave, and has various types of waveform. Specifically, the arc signal is similar to the driving pulse, which is created in appliances, such as an electric fan and dryer, which have an electric motor inside.
Also, if you use an electrical device, at the beginning of a cycle, a high pulse similar to the arc signal is generated, but after some time passes, the output signal has a normal amplitude. Therefore, it is difficult to detect arcing because the arc signal is similar to driving pulse at the beginning of a cycle.
The arc fault detector (AFD) disclosed in U.S. Pat. No. 5,805,397 uses a method of detecting arcing by multiple channel sensing. The prior patent discloses the method of detecting arcing in several bandwidths, and the AFD trips the circuit in a condition of arcing generation in all of the bandwidths.
A schematic diagram in block form of the prior art is shown in FIG. 1. The electrical system 100 protected by the circuit breaker 103 includes a line conductor 105 and a neutral conductor 107 connected to provide power to a load 109. The circuit breaker 103 includes separable contacts 111 that can be tripped open by a spring operated by trip mechanism 101. The trip mechanism 101 may be actuated by a conventional thermal-magnetic overcurrent device 116. This thermal-magnetic overcurrent device 116 includes a bimetal connected in series with the line conductor 105. Persistent overcurrents heat up the bimetal causing it to bend and release a latch 113, which actuates the trip mechanism 101. Short circuit currents through the bimetal 115 magnetically attract an armature 114, which alternatively releases the latch 113 to actuate the trip mechanism 101.
A schematic diagram of a prior art arc fault detection circuit is shown in FIG. 2. The arc fault detector 120 is a multi-channel bandpass filter circuit 121, which includes two channel 123, 124. The channels 123, 124 includes respectively bandpass filters 125, 126. Each bandpass filter 125, 126 has an assigned, distinct non-overlapping passband. Thus, each of the bandpass filters 125, 126 will generate an output signal in response to an are fault. Therefore the circuit breaker is tripped when the output signal, which is obtained by summing the output of the filters 125, 126 reaches at a specified level.
A block diagram illustrating an arc fault/ground fault circuit interrupter (AFCI/GFCI) device of the other prior art is shown in FIG. 3. The prior AFCI generates output signal by comparing the first arc detecting signal in the line with the second arc detecting signal in the load. The AFCI/GFCI device 180 comprises AFCI/GFCI circuitry 182, line circuitry 188, load circuitry 200, arc detection circuitry 198, local/remote inhibit circuitry 184, and timer circuitry 186. The prior art AFCI/GFCI device detects arcing faults in the line area and load area using many different elements and making the device more complex. Thus, it greatly increase efforts and the cost demanded for production. The prior art AFCI/GFCI device may control processing of electric circuits independently in response to arc generation, resulting in the comparison of line arcing and load arcing at each of line circuitry 188 and load circuitry 200. However, the prior art needs an amplifier, filter, rectifier and peak detector at both the line and the load circuitry, so more cost is incurred. Furthermore, it is difficult to install an AFCI/GFCI device in a residential place because of its large size.
Moreover, various electrical devices in addition to circuit breaker include one or more elements that protect the electrical devices or inner circuit of itself respectively from heat or damage resulting from an overload. Generally, this element is a bimetal that comprises two metallic plates, as it were, high and low expansion plates which have different coefficients of heat expansion, attached to each other by a rolling method. Each metallic plate is bent to a different degree by temperature variation. The bimetal is widely used as thermometer or automatic operational switch because it bends with relative ease even when subjected to only a small variation in temperature. More particularly, if the temperature of the bimetal increases because overcurrent is passing through an electrical device, it bends toward the side of the low expansion plate and the electrical device is interrupted. The low expansion metallic plate has a very low coefficient of heat expansion and the high expansion metallic plate has a high coefficient of heat expansion. Some alloys used for producing high expansion metallic plates are nickel-chrome-iron alloy, nickel-manganese-iron alloy, or manganese-copper-nickel alloy.
In the United States, there are various regulations controlling the triggering of a circuit breaker. For example, the circuit breaker must be triggered within 1 hour in the case of 135% current flow, and 4 minutes in the case of 200% current flow rated current for AC 120 volts, 15 or 20 A. However, because overcurrent passes through the bimetal sequentially for the test time (1 hour or 4 minutes), the duration of circuit breaker tests is long and expensive. Also, the bending characteristics of the bimetal easily change with time and use. Therefore, it is difficult to detect overload consistently since an operational feature of the circuit breaker is changed as time passes. Also, after the bimetal bends once because of an overload on it, it takes a long time to reset. Thus, there is loss of time and increased cost involved in the normal operation of the circuit breaker followed by the bending of the bimetal. Also, under various real conditions, the prior arts cannot detect an arc fault and overload, so, they cannot prevent fires from occurring in residential or commercial buildings.
The arc fault circuit interrupter (AFCI) of the present invention can effectively detect an arc fault generated in an electrical system, and so protect people and property from fire.
Also, the overload circuit interrupter (OLCI) of the present invention can detect an overload in an electrical system and can trip the electrical system electrically. The OLCI does use a mechanical device such as a bimetal, so the cost and time needed for testing circuit breaker is minimized. Also, initialization of the OLCI is accomplished at the same time the circuit breaker is tripped.
The AFCI and the OLCI of the present invention can operate in combination with a ground fault circuit interrupter (GFCI). Thus, a circuit breaker with an AFCI, GFCI and OLCI of the present invention can be provided to detect an arc fault, ground fault and overload effectively. Also, the circuit breaker is relatively small and so can be installed easily in a residential or commercial building.
Also, the circuit breaker includes a capacitor, which discharges voltage caused by arc fault, ground fault or overload correctly through the triggering of a power switch. Thus, it is possible to detect arc fault, ground fault or overload successively, and, it is easy to test the operation of the circuit breaker.
To achieve the above-mentioned objects of the present invention, provided is an overload circuit interrupter (OLCI) device in an electrical wiring system that can shut an AC (Alternating Current) source off from a phase conductor and a neutral conductor when an arc fault occurs in the AC source. The overload circuit interrupter (OLCI) may include a current transformer for producing an overload voltage in accordance with the variation of the phase conductor and in the neutral conductor, a rectifier for half-or full-wave rectifying the overload voltage, a level controller for limiting the rectified overload voltage to a specified level, an integrator for charging the limited overload voltage from the level controller and for providing an overload indicative signal, and a comparator for comparing the overload indicative signal with a reference overload voltage and for producing an overload trip signal, which shuts the AC source off from the phase conductor and the neutral conductor.
The rectifier may comprise a plurality of diodes coupled to the current transformer. The level controller may comprise a coupling element for controlling the level of the rectified overload voltage, and a buffer for delaying the charged overload voltage. The comparator may comprise an operational amplifier. The OLCI may further comprise a reference voltage generator for generating the reference overload voltage. The OLCI may further comprise a bias generator for generating a bias provided to the comparator together with the overload indicative signal. The OLCI may further comprise a discharge controller for discharging the voltage from said integrator when the AC source shuts off.
To achieve the above-mentioned objects of the present invention, also provided is a circuit breaker in an electrical wiring system that can shut an AC source off from a phase conductor and a neutral conductor when an overload occurs in the AC source. The circuit breaker may comprise an overload circuit interrupter (OLCI) coupled to the phase conductor and the neutral conductor for detecting an overload and producing an overload trip signal, a display circuitry for indicating the overload corresponding with the overload trip signal, and a trip circuitry coupled to the phase conductor and the neutral conductor, for shutting the AC source off from the phase conductor and the neutral conductor when an overload trip signal is provided, wherein the OLCI may include a current transformer for producing an overload voltage in accordance with the variation of the phase conductor and in the neutral conductor, a rectifier for half-or full-wave rectifying the overload voltage, a level controller for limiting the rectified overload voltage to a specified level, an integrator for charging the limited overload voltage from the level controller and for providing an overload indicative signal, and a comparator for comparing the overload indicative signal with a reference overload voltage and for producing an overload trip signal, which shuts the AC source off from the phase conductor and the neutral conductor.
Also, to achieve the above-mentioned objects of the present invention, provided is an arc fault circuit interrupter (AFCI) in an electrical wiring system that can shut an AC source off from a phase conductor and a neutral conductor when an arc fault occurs in the AC source. The AFCI may comprise a first current transformer for producing an arc fault voltage in accordance with the variation of current in the phase conductor and in the neutral conductor, a rectifier for half- or full-wave rectifying of the arc fault voltage, a first buffer for delaying the rectified arc fault voltage, a first comparator for comparing the rectified arc fault voltage with a first reference voltage and producing an arc fault indicative signal, an integrator for charging the arc fault indicative signal from the first comparator, and a second comparator for comparing the arc fault indicative signal with a second reference voltage and producing an arc fault trip signal.
Also, to achieve the above-mentioned objects of the present invention, there is provided a circuit breaker in an electrical wiring system that can shut an AC source off from a phase conductor and a neutral conductor when an arc fault occurs in the AC source. The circuit breaker may comprise an arc fault circuit interrupter (AFCI) coupled to the phase conductor and the neutral conductor for detecting an arc fault and producing an arc fault trip signal, a display circuitry for indicating the arc fault corresponding with the arc fault trip signal, and a trip circuitry coupled to the phase conductor and the neutral conductor, for shutting the AC source off from the phase conductor and the neutral conductor corresponding with the arc fault trip signal, wherein the AFCI may include a first current transformer for producing an arc fault voltage in accordance with the variation of current in the phase conductor and in the neutral conductor, a rectifier for half- or full-wave rectifying of the arc fault voltage, a first buffer for delaying the rectified arc fault voltage, a first comparator for comparing the rectified arc fault voltage with a first reference voltage and producing an arc fault indicative signal, an integrator for charging the arc fault indicative signal from the first comparator, and a second comparator for comparing the arc fault indicative signal with a second reference voltage and producing an arc fault trip signal.
Also, to achieve the above-mentioned objects of the present invention, there is provided a circuit breaker in an electrical wiring system that can shut an AC source off from a phase conductor and a neutral conductor when an overload occurs in the AC source. The circuit breaker may comprises an arc fault circuit interrupter (AFCI) coupled to the phase conductor and the neutral conductor for detecting an arc fault and producing an arc fault trip signal, an overload circuit interrupter (OLCI) coupled to the phase conductor and the neutral conductor for detecting an overload and producing an overload trip signal, a display circuitry for indicating the arc fault or overload corresponding with the arc fault trip signal or overload trip signal, and a trip circuitry coupled to the phase conductor and the neutral conductor, for shutting the AC source off from the phase conductor and the neutral conductor corresponding with the arc fault trip signal or overload trip signal, wherein the AFCI may include a first current transformer for producing an arc fault voltage in accordance with the variation of current in the phase conductor and in the neutral conductor, a rectifier for half-or full-wave rectifying the arc fault voltage, a first buffer for delaying the rectified arc fault voltage, a first comparator for comparing the rectified arc fault voltage with a first reference voltage and producing an arc fault indicative signal, an integrator for charging the arc fault indicative signal from the first comparator, and a second comparator for comparing the arc fault indicative signal with a second reference voltage and producing an arc fault trip signal, and wherein the OLCI may include a current transformer for producing an overload voltage in accordance with the variation of the phase conductor and in the neutral conductor, a rectifier for half-or full-wave rectifying the overload voltage, a level controller for limiting the rectified overload voltage to a specified level, an integrator for charging the limited overload voltage from the level controller and for providing overload indicative signal, and a comparator for comparing the overload indicative signal with a reference overload voltage and producing an overload trip signal, which shuts the AC source off from the phase conductor and the neutral conductor.
Also, to achieve the above-mentioned objects of the present invention, there is provided a circuit breaker in an electrical wiring system that can shut an AC source off from a phase conductor and a neutral conductor when an overload occurs in the AC source. The circuit breaker may comprises an arc fault circuit interrupter (AFCI) coupled to the phase conductor and the neutral conductor for detecting an arc fault and producing an arc fault trip signal, an overload circuit interrupter (OLCI) coupled to the phase conductor and the neutral conductor for detecting an overload and producing an overload trip signal, a ground fault circuit interrupter (GFCI) coupled to the phase conductor and the neutral conductor for detecting a ground fault and producing a ground fault trip signal, a display circuitry for indicating the arc fault, ground fault or overload corresponding with at least one selected from the group consisting of the arc fault trip signal, the ground fault trip signal and the overload trip signal; and a trip circuitry coupled to the phase conductor and the neutral conductor, for shutting the AC source off from the phase conductor and the neutral conductor corresponding with at least one selected from the group consisting of the arc fault trip signal, the ground fault trip signal and the overload trip signal.